The present disclosure relates generally to the field of automated maintenance (including non-destructive inspection) of aircraft structural elements such as airfoil-shaped bodies, and more particularly to an automated end effector-carrying apparatus that is coupled to and travels along an airfoil-shaped body having a relatively short chord length, such as a rotorcraft blade, an aircraft propeller blade, a winglet, a projectile fin, an aircraft horizontal stabilizer, etc., while performing a maintenance function. As used herein, the term “maintenance” includes, but is not limited to, operations such as non-destructive inspection (NDI), drilling, scarfing, grinding (e.g., to remove bonded or bolted components), fastening, appliqué application, ply mapping, depainting, cleaning and painting.
In order to provide maintenance for airfoil-shaped bodies such as blade components, it is known to manually remove the blade components from the aircraft and then manually perform the maintenance functions. Removal of blade components from an aircraft is cost intensive. With helicopter blades, for example, the time spent removing, transporting, re-attaching, balancing and trimming the blades can be significant. Some helicopters require that the blades be removed and inspected every 50-75 flight hours, resulting in a dramatically reduced mission capability of the aircraft.
Furthermore, performing maintenance functions manually uses skilled technicians. These technicians are in short supply; therefore the labor cost to manually perform maintenance functions is significant. Because manual maintenance is complex and repetitive, the likelihood of human error is high. When a repetitive maintenance operation is botched by a human, the flawed blade component could be reattached to the aircraft with a dangerous flaw still imbedded in the component.
Surface-riding probes in gimbaled holders have been used in the non-destructive inspection of composite aerospace hardware in some gantry-type systems. These systems generally use some level of “teaching” of the scanner to get close enough to the contour, and the gimbaling of the shoe handles the difference. They are usually using pulse-echo ultrasound, so the sensor or riding shoe can rest directly on the surface. Besides requiring “teaching”, these probes/shoes do not handle significant contours—like those on a rotorcraft blade leading edge—very well. One known scanning system has a spring-loaded shoe that works well for minor contours, but will not work for rotorcraft blades, particularly with sensors that have “feet” on them, because they tend to tip over.
Another apparatus for providing automated movement of a non-destructive inspection (NDI) sensor over a surface of an airfoil-shaped body is disclosed in U.S. Pat. No. 8,347,746. The apparatus in accordance with one embodiment comprises a “blade crawler” that travels in a spanwise direction along a rotorcraft blade. The blade crawler in turn has means for moving an NDI sensor in a chordwise direction. The respective movements in the spanwise and chordwise directions enable the sensor to be rastered over the surface of the rotorcraft blade.
The foregoing “blade crawler” automates what has been a slow and tedious hand-held inspection operation for rotorcraft blades, while allowing the rotorcraft blades to remain on the rotorcraft. However, there are challenges with automated rastering of a sensor on a non-planar surface such as the surface of a rotorcraft blade. While aircraft wings and fuselages have gradual contours, rotorcraft blades have surfaces with more significant contours that may use new fixturing if automation is to be achieved. In addition, the optimum sensors for some rotorcraft blade inspection are pitch-catch sensors, which have several individual “contact feet” on them that make them prone to falling over.
It would therefore be highly desirable to have an automated apparatus capable of scanning airfoil-shaped bodies having short chord lengths and significant contours while adjusting the orientation of the end effector (e.g., an NDI sensor or sensor array) during movement over the contoured surface.